Well here is a diagram from the
eper of the fuel tank setup..
I presume the pipe you keep referring to to no.4 - that is the tank breather for when you are filling up, you see it goes across and joins a small pipe on the filler neck. That is to release pressure as you fill up with fuel at the petrol station..
Without seeing it its really hard to say anything at all for certain. But my first thoughts would be, what has been used to repair that pipe, is said product going to last with permanent contact with petrol cause not alot of glues are..
After that I would be checking the seals at the end of that pipe are both still there, easy to lose one of them when the pipe is removed - so check they are still there and are they still looking ok and not all hard and cracked?? These bits are still available new from fiat i believe but a very quick google came up with some cheap on Italian ebay -
http://www.ebay.com/itm/7628223-PAK...K-FIAT-PUNTO-FIORINO-LANCIA-Y10-/360857289680
I'd next look at the little valve (no.18) and its seal (no.20) - Now I have never messed with this and not 100% what its for - relieving pressure when ca is not running perhaps? It doesn't really matter though, due to where it is I can see that leaking if the car was full of fuel and on a slight angle - check the seal for that. Again quick search is bring both these parts up on german and/or italian ebay but i stress I am not looking hard just throwing the part numbers into google. My
eper though (2014 version) is saying all 3 bits I have mentioned are still available new.
part numbers:
valve (no. 18) - 46415700
valve seal (no. 20) - 7700824
breather pipe seals (no. 22) - 7628223
All this is a pain I'll grant you as you kinda need to drop the tank to check any of it and then refit and fill up to test it properly. So really the easiest thing to do is to replace anything that you are even remotely suspect about. Sadly the breather pipe itself is not available new but i'm sure its possible to find a suitable hose thats fuel resistant to replace it rather than try fix it - if you have a search around for flexible fuel filler hose you will prob find something suitable i should think - something like this
http://www.asap-supplies.com/seaflow-iso7840-fuel-hose-305825. You will of course have to get a actual measurement of the pipe ID first though.